The present invention relates to delivery systems for liquid phosphorous precursors, and in particular to stainless steel containers, piping and injection valves for injecting liquid triethylphosphate (TEPO), TMP or TEP into a chemical vapor deposition (CVD) chamber.
A variety of different systems can be used to deliver processing gases to a chemical vapor reaction chamber. In a boiler system, the liquid is heated into vapor form. In a xe2x80x9cbubblerxe2x80x9d system, gaseous helium is introduced into a liquid in a container, resulting in some of the liquid being bubbled out of solution. When the liquid contains a phosphorous precursor, such as TEPO, TMP or TEP, and the container or piping is stainless steel, residue build-up has been observed, in particular where the stainless steel is exposed to heat.
Injection valves are often used for providing a processing gas to a CVD chamber. In one method of doing this, the active gas component is provided in liquid form to an injection valve. The injection valve provides the liquid through an orifice past which a carrier gas is provided. A pressure drop is created which causes the liquid to vaporize into gaseous form. Typically, a heater is also provided on the valve to prevent condensation of the processing gas. A typical inert carrier gas is helium.
One problem encountered with such valves is the build-up of residue around the orifice, which can prevent proper seating of a cut-off plug to hinder control of the valve. Excessive build-up of residue can also block the orifice itself, or severely restrict the flow of liquid through the orifice. Residue build-up on other surfaces can contaminate subsequent gases flowing across the surface or contained in the container.
Accordingly, it would be desirable to have an liquid phosphorous precursor delivery system which minimizes the build-up of residue on stainless steel surfaces.
The present invention recognizes that the build-up of residue in a metal alloy injection valve used to inject a liquid phosphorous precursor compound is due to the nickel in the alloy affecting the liquid phosphorous precursor compound. The invention thus provides components manufactured of an alloy having a low nickel content, preferably less than 5% nickel, and more preferably less than 1%. In an additional aspect of the invention, the alloy is provided with a higher chromium content, preferably at least 15% chromium, more preferably 16-27%.
The chromium appears to inhibit the leaching of the metal by the liquid phosphorous precursor compound, thus preventing the nickel being leached out of the metal to affect the liquid phosphorous precursor compound. The nickel appears to act as a catalyst for causing decomposition of the phosphorous precursor compound when heated. Preferably, the components exposed to the phosphorous precursor compound and heat are made of stainless steel alloys of standard industrial designations 430, 440, or 446, which all have a nickel content of less than 1%.
In one embodiment, an injection valve is made of stainless steel alloys of standard industrial designations 430, 440, or 446. This alloy is preferably used for the body of the valve, but in particular for at least the portions of the valve around the injection orifice.
In another embodiment, a polymides used for a plug in an injection valve instead of prior art fluoropolymers. The polymide, preferably VESPEL(copyright)(a Du Pont product) is used, and exhibits better tolerance to the liquid phosphorous precursor compound and heat. The polymide can also be used for gaskets and seals.